The present invention relates to a power converter for an LED assembly, the power converter comprising an AC/DC converter and a switched mode power supply for powering the LED assembly. The present invention further relates to a lighting application comprising a power converter and an LED assembly.
At present, in architectural and entertainment lighting applications more and more solid state lighting based on Light Emitting Diodes (LED) is used. LEDs or LED units have several advantages over incandescent lighting, such as higher power to light conversion efficiency, faster and more precise lighting intensity and colour control by providing a current flowing through the LEDs.
In order to provide said current through the LED or LEDs, a power supply such as a switched mode power supply (or a regulator such as a linear regulator) can be used. Examples of such switched mode power supplies (SMPS) are e.g. Buck, Boost or Buck-Boost converters. Such converters are also referred to as switched mode current sources or switched mode voltage sources. In general, such a converter requires a DC input voltage, that can be provided by an AC/DC converter. Such an SMPS may then be used to provide a substantially constant current to an LED assembly comprising one or more LED units. When such an LED unit comprises LEDs of different colour, the resulting colour provided by the LED unit can be modified by changing the intensity of the different LEDs of the unit. This is, in general, done by changing the duty cycles of the different LEDs. Operating the LEDs at a duty cycle less than 100%, can be achieved by selectively (over time) providing a current to the LEDs, i.e. providing the LEDs with current pulses rather than with a continuous current. By appropriate selection of the duty cycle a required colour and intensity can be provided. In order to provide a high resolution with respect to the intensity or colour of the light source, a precise control of the current pulses is required to enable high-resolution LED lighting colour or white mixing control. A switched mode power supply (e.g. a buck converter) can e.g. be powered from a fixed DC voltage source (e.g. a battery) or from an AC/DC converter which converts an AC voltage (e.g. from a mains supply) to a suitable DC voltage that can be used as a supply voltage for the SMPS. In general, an AC/DC converter provides a substantially fixed DC output voltage to the SMPS. Depending on the desired output characteristic of the LED assembly (e.g. a very bright light or a dimmed light) the load represented by the LED assembly for the SMPS may vary substantially. In particular, the forward voltage over the LED assembly (also referred to as the load voltage) may vary substantially, depending on the desired output characteristic. This is in particularly true in case multiple LED units are connected in series. Due to this variable load voltage, the operating conditions of the SMPS may vary substantially. In particular, it can be stated that the efficiency of the SMPS may vary considerably depending on the operating conditions as imposed by the load (i.e. the LED assembly).
In view of this, it is an object of the present invention to provide a power converter for an LED assembly that is adjustable to varying load conditions presented by the LED assembly.